The present invention relates to phase-change memories. In particular, a system and method of operation are provided for the phase-change memory cells using an adjusted power heating pulse to avoid under- and over-heating. Phase-change materials may exhibit at least two different states. Consequently, phase-change material may be used in a memory cell to store a bit of data. The states of a phase change material may be referred to as amorphous and crystalline states. These states may be distinguished because the amorphous state generally exhibits higher resistivity than does the crystalline state. Generally, the amorphous state involves a more disordered atomic structure, while the crystalline state features an ordered lattice.
Phase change in the phase-change materials may be induced reversibly. In this way, the memory may change from the amorphous to the crystalline state, and vise versa, in response to temperature changes. The temperature changes to the phase-change material may be effectuated in a variety of ways. For example, a laser can be directed to the phase-change material, current may be driven through the phase change material, or current or voltage can be fed through a resistive heater adjacent the phase change material. With any of these methods, controllably heating the phase-change material causes controllable phase change with the phase-change material.
When a phase-change memory comprises a memory array having a plurality of memory cells that are made of phase-change memory material, the memory may be programmed to store data utilizing the memory states of the phase-change material. One way to read and write data in such a phase-change memory device is to control a current (or a voltage) that is directed through the phase-change material, or through a heater adjacent to it. Since the switching in such memory cells depends on the exact temperature of the phase-change memory material, it is necessary to control temperature within each memory cell, independent of ambient conditions. For these and other reasons, there is a need for the present invention.